What is the difference between P0405 and P0406?

P0405 means the signal is too low (below ~0.2V), usually a short to ground or failed sensor. P0406 means the signal is too high (above ~4.5V), usually an open wire, missing ground, or a sensor that has failed internally. Diagnostic steps are similar but the failure modes are opposite.

Can I drive with P0406?

Yes, short distances. The ECU disables EGR control, so the engine runs without EGR. Expect rough idle and possible limp mode on diesels. Long-term driving accelerates intake carbon buildup, especially on direct-injection engines. Plan the repair within a few weeks.

Is EGR delete a legal workaround for P0406?

No. Deleting the EGR system invalidates the vehicle's emissions type approval, which is why it is prohibited across the EU and in the UK. It raises NOx output above the limits the engine was homologated to, and an inspector who finds it has grounds to reject the car under whichever national roadworthiness rules apply. It can also void insurance and block a registration transfer. Always repair the sensor or valve properly.

Why does P0406 come back after I replaced the sensor?

Two common reasons. First, the EGR adaptation was not carried out after the new valve was fitted; on many BMW, Mercedes and VW Group engines this needs manufacturer-level software, not a generic OBD2 reader. Second, the carbon buildup that caused the original sensor stress is still present and damages the new sensor within months. Always clean the intake passages alongside any valve replacement.

P0406: Exhaust Gas Recirculation Sensor "A" Circuit High

Quick Answer

Safe to drive (short-term)

P0406 means EGR position sensor 'A' is sending a voltage above its normal operating range, typically above 4.5V. This is usually caused by an open signal or ground wire, a short to the 5V reference, or a sensor that has failed internally and drives its signal high.

Severity: Moderate · Emissions
Estimated repair cost: From €70 to €670+, varies by vehicle

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What does P0406 mean?

P0406 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0406 and illuminates the check engine light.

Where it is on the car

Engine
Exhaust manifold
EGR cooler (diesels and many newer petrols)
EGR valve and position sensor
Intake manifold

What are the symptoms of P0406?

If your vehicle has triggered P0406, you may notice one or more of these symptoms:

Check engine light illuminated
Rough idle, sometimes stalling at stops
Reduced power on diesels (limp mode)
Hesitation during light throttle
Rejection at an emissions test or periodic technical inspection

What causes P0406?

Here are the most common causes of P0406:

EGR position sensor failed internally, driving its signal towards the 5V reference
: high
Open or broken signal wire between sensor and ECU
: high
Loose or unseated EGR sensor connector
: medium
Carbon buildup holding valve at maximum reported position
: medium
Open ground circuit on the sensor side
: low

Is it safe to drive with P0406?

Generally yes, for short-term driving. Driveable. P0406 means the EGR position sensor (sensor A) is reporting a voltage higher than the expected range. The ECU loses trust in the EGR feedback and disables the system, causing rough idle and possible limp mode on diesels. With the warning light on, the fault can be recorded as a deficiency at a periodic inspection.

How do you diagnose P0406?

Follow these steps to pinpoint the root cause of P0406:

Back-probe the sensor signal wire at the sensor with the key on, engine off. A reading near 5V there with the valve closed points to the sensor or a short to the reference; a normal reading at the sensor but a high value in live data points to a break in the signal wire towards the ECU
Verify the sensor ground at the connector. If ground is missing, the signal will float high
Unplug the connector and check for damaged pins or unseated terminals
Check the signal wire for continuity between the sensor connector and the ECU, and for a short to the 5V reference or battery voltage. Use the wiring diagram to see how the ECU treats an unplugged input, because whether it floats high or low depends on the ECU design
If wiring and ground are good and the sensor reads 5V steadily, the integrated sensor has failed. Replace the EGR valve assembly

How much does P0406 cost to fix?

Repair costs for P0406 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Re-seat and clean EGR sensor connector	€10–€60	€60–€180	€70–€240	Moderate
Replace EGR valve (sensor integrated)	€150–€450	€80–€220	€230–€670	Moderate
Repair EGR wiring harness or signal wire	€20–€120	€120–€350	€140–€470	Professional

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

EGR Valve Replacement Cost

P0406 on specific vehicles

P0406 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0406 on BMW

BMW 3 Series

See BMW-specific causes & cost

P0406 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

P0406 on Audi

Audi A4

See Audi-specific causes & cost

P0406 on Mercedes-Benz

Mercedes Sprinter

See Mercedes-Benz-specific causes & cost

These codes are often seen alongside P0406 or indicate related issues:

Common questions about P0406

What is the difference between P0405 and P0406?: P0405 means the signal is too low (below ~0.2V), usually a short to ground or failed sensor. P0406 means the signal is too high (above ~4.5V), usually an open wire, missing ground, or a sensor that has failed internally. Diagnostic steps are similar but the failure modes are opposite.
Can I drive with P0406?: Yes, short distances. The ECU disables EGR control, so the engine runs without EGR. Expect rough idle and possible limp mode on diesels. Long-term driving accelerates intake carbon buildup, especially on direct-injection engines. Plan the repair within a few weeks.
Is EGR delete a legal workaround for P0406?: No. Deleting the EGR system invalidates the vehicle's emissions type approval, which is why it is prohibited across the EU and in the UK. It raises NOx output above the limits the engine was homologated to, and an inspector who finds it has grounds to reject the car under whichever national roadworthiness rules apply. It can also void insurance and block a registration transfer. Always repair the sensor or valve properly.
Why does P0406 come back after I replaced the sensor?: Two common reasons. First, the EGR adaptation was not carried out after the new valve was fitted; on many BMW, Mercedes and VW Group engines this needs manufacturer-level software, not a generic OBD2 reader. Second, the carbon buildup that caused the original sensor stress is still present and damages the new sensor within months. Always clean the intake passages alongside any valve replacement.

Read our detailed guides

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